Motor learning – It’s good being in the background

This was a story I first saw on Digg today but it’s worth posting about here. Researchers at MIT recently published a study in Neuron (May 24, 2007 issue) that demonstrates a completely new way of looking at motor learning. From their article:

“In experiments on motor learning, it is often assumed that there is an underlying neural representation that is stable and that adaptation takes place on top of this stable background. Our experimental and theoretical results suggest a radically different picture. The experiments show that tuning curves of motor cortical cells are constantly changing even when performing a familiar task. Furthermore, when learning a new task, learning-related changes occur on top of this background of changing tuning curves” (Rokni, Richardson, Bizzi, & Seung, 2007, p. 661).

They are proposing that the neuronal activity associated with motor learning is a little like a sail-less ship on the ocean. This ship not only goes up and down the waves as they come, it also drifts about somewhat randomly in response to the underlying and unstable movement of the water underneath. This analogy isn’t perfect but it is OK.

Learning is not only a component of the active responsive brain activity but also the somewhat random low-level “background noise” that is slowly “retuned” and “retunes” in response to motor learning. This background noise only affects the synapses very slowly but it has a noticeable effect: “According to our theory, this slowness is necessary to prevent the noise from erasing motor memories” (p. 663). They do believe that this unstable foundation for learning is linked to forgetting over time. The researchers also state that there may be many ways that neurons can represent essentially the same behavior: “any single behavior can be realized by multiple configurations of synaptic strengths” (p. 653).